Mixing impellers are in wide use in industry. Examples of industrial mixing impellers include designs which have a central hub and two, three, four or more radially extending blade type structures. These blades may be flat, angled, and in some cases have a wing or propeller shape. Typically, the impellers extend radially outwardly from a motor-driven shaft and are submerged inside a material to be mixed. Oftentimes the impellers are in an at least partially liquid mix which is being confined in a vessel, which may be holding the material in a batch process or a continuous process.
In some mixing applications, an undesirable phenomenon occurs wherein various solid materials that are entrained in the liquid material being mixed will tend to accumulate on a leading edge of the impeller and form lumps, strings, or so-called “rags.” One way to understand this phenomenon is to consider impellers used on boats, which will capture weeds that adhere to a leading edge of the boat propeller and impede its operational efficiency. Similarly, a ceiling fan often accumulates dust on its leading edge which will form into elongated filaments or streams.
A similar phenomenon occurs, particularly, for example, in the case of mixing impellers used for wastewater or sewage water treatment, wherein the material being mixed often has various types of crud, solid particulates, hair and other non-dissolving material. As the water is being treated, these materials may tend to adhere to the leading edge of existing impellers, which reduces the flow over the impeller type, and reduces the efficiency of the impeller and may cause overload, vibration and possible damage to the equipment.
In many industrial applications, the impellers are so-called “axial flow” in which the liquid in the region of the impeller is being pumped in the direction generally parallel to the axis of the drive shaft (perpendicular to the direction of the extensions of the blades). In other instances, the impellers may be the so-called “radial flow” type, in which the material is generally being urged radially outwardly away from the drive shaft in a direction parallel to the direction of the extensions of the blades. Some impellers have been known to utilize a circular base having paddles radially extending outwardly therefrom.
In view of the foregoing, it is desirable to have a “weedless” mixing impeller that can mitigate, at least to some extent, the effect of the development of “rags” or other collections adhering to the leading edge of the impeller, or to any edge of the impeller.